40 CLASS REPTILIA. 



lary bone only. Under the tooth is a gland which secretes the 



poison. 



- The teeth of frogs, toads, &c., are very short, and almost 



reduced to nothing. 



Almost all reptiles live on animal substances ; for scarcely 

 any, except some tortoises, feed on algae, fucus, &c. Accord- 

 ingly, their stomach is more capacious than that of other rep- 

 tiles. Frogs, and the majority of lizards, feed on insects and 

 worms, which they catch with their gluey tongues. The 

 larger species of lizards, such as crocodiles, swallow other 

 animals. Serpents seek for their food animals of all species, 

 whose size is not too disproportioned with their own. The 

 stomach of all reptiles has but poor digestive powers, espe- 

 cially in the order of serpents, in which it forms a sort of 

 membraneous funnel. All reptiles, except the tortoise, are 

 destitute of coeca. 



The skeleton of reptiles is not so hard as that of warm- 

 blooded animals. Their bones contain less phosphate of 

 lime, and the gelatinous matter is more abundant, especially 

 in frogs and salamanders. 



The limbs of reptiles vary in their forms, proportions, and 

 number. The tortoises and lizards have four, and also a 

 tail. There are no ribs in the batracians. They have four 

 legs : but the salamanders alone have a tail. These and 

 frogs are remarkable in their first age for breathing by gills, 

 like fishes. Their mode of circulation is then similar to that 

 of fishes, and their intestines are considerably extended, and 

 destined to digest vegetable nutriment ; but they are after- 

 wards transformed into their last state, and changed not only 

 externally, losing their gills, but also, internally, as to the 

 constitution of their viscera. They no longer seek vegetable 

 aliment as before — animal food becomes necessary to their 

 subsistence. There are, however, two genera in the order of 



